This invention relates to a solenoid actuator and particularly to one that has an axially movable armature having two stable operating positions.
Modern motor vehicles include numerous features and conveniences for enhanced occupant comfort, convenience, and security. One such feature is the provision of a lockable fuel filler door. Many passenger cars have a hinged filler door in the rear quarter panel or rear trunk area which encloses the fuel tank filler cap. As a means of preventing theft of fuel or the introduction of contaminants into the tank, many cars are equipped with a fuel filler door that is lockable. One type of lockable filler door has its own key and tumbler locking mechanism. This type requires the use of a key to unlock the filler door in order to fill the fuel tank. As a means of providing a more convenient lockable fuel filler door, various approaches for coordinating the locking of the vehicle doors with the fuel filler tank have been devised. One such system uses a small electric motor which operates remotely through a flexible cable to move a filler door latch between locked and unlocked positions. Remote mounting of the actuation motor is used to simplify installation of the actuator and to avoid the presentation of electrical sparks near flammable vapors vented from the fuel tank. Although such devices operate satisfactorily, there is a continuing desire to reduce their cost and enhance their performance.
Although solenoid type actuators inherently have an advantage over electric motors in terms of cost and simplicity, they have the inherent disadvantage that their axially movable armature is ordinarily stable in only one operating position. In order to maintain the solenoid armature at a position displaced from its stable position, a constant current flow is ordinarily required. In motor vehicle applications, it is desirable to minimize electrical current demand to reduce alternator loads, and further, to prevent battery depletion when the vehicle is not being operated. Accordingly, there is a need for a solenoid operated actuator which has a movable armature with two stable positions which do not require current flow except during periods wherein the state of the solenoid is being changed.